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From: hutch@celerity.uucp (Jim Hutchison)
Newsgroups: comp.arch
Subject: Re: IPI-2 vs. SCSI
Message-ID: <564@celit.UUCP>
Date: 22 Aug 89 19:33:30 GMT
References: <13698@polyslo.CalPoly.EDU>
Reply-To: hutch@celerity.UUCP (Jim Hutchison)
Distribution: na
Organization: FPS Computing
Lines: 46

Lets start by noting that IPI is not a bright-shiny-new interface, but
a set of interfaces which have been in use by folks like Burroughs, Gould,
and IBM for a while now.  IPI-2 is akin to a better SMD, and IPI-3 is akin
to a better SCSI.

>[...] I guess Imprimis has announced an
>8in. drive w/ dual read channels capable of 6 MB/s, sustained or
>peak I'm not sure, and a native IPI-2 interface. Not bad :)

Lock 2 heads together, and *poof* HSMD disk technology becomes 6 Mbyte/s
with a new cable/electronics which send byte data instead of
clock/data/control.  IPI-2 disks are not limited to 6 Mbyte/s (like SCSI),
they are limited by a "new" number of ~30 Mbyte/s.  IPI-3 has a similar
cable/driver based limit.

>   But why go with an under-developed interface such as IPI-2 ?
Basis for this statement please?

>SCSI has a lot of software supporting it which implies it is reasonably
>well understood; you can get cheap SCSI protocol IC's that'll go
>5 MB/s; and the prices are lessening as momentum picks up.

Bulk software == well understood, maybe.  Is it documentation you lack?
SMD is also well understood, but people are getting tired of the low
bandwidth (<3 Mbyte/s).

>   Both IPI and SCSI have upgrades in the planning process. SCSI
>plans to go 40 MB/s (through "wide" and "fast") and IPI is projected
>to go 50 MB/s with a max cable length of 50m when ECL drivers are
>used. Someday IPI may [...]

Good to hear they are both still moving forward.  I'm a bit puzzled
by the wide (32bit) and fast SCSIs.  They will probably kill the SCSI
market by confusing people.  I personally would get miffed if I got
a wide/fast interface and the *wrong* kind of SCSI disk.  At the moment
it would appear that IPI-3 has SCSI pegged with its ability to have
a device decide what clock rate it wants for data.  This allows for
faster equipment in the future without causing peoples hair to friz
with compatibility problems within the *standard* interface.

As to the comment on single-source IPI chips being grossly expensive,
I'm not to amazed.  They've got the market, "why not milk it".  When
competition starts, prices whould drop.

/*    Jim Hutchison   		{dcdwest,ucbvax}!ucsd!celerity!hutch  */
/*    Disclaimer:  I am not an official spokesman for FPS computing   */